Proper soil compaction is critical to providing adequate structural support in any geo-construction project, and is particularly relevant to road construction. The past decade has brought significant advances in earthwork compaction quality control/quality assurance (QC/QA). The most notable advance has been the introduction of roller compactor-integrated measurement of soil stiffness coupled with GPS-based documentation. Through measurement of drum vibration, roller-integrated measurement systems continuously report on the stiffness of the underlying soil. The combination of roller integrated measurement and GPS based mapping and documentation, referred to as continuous compaction control (CCC) or intelligent compaction (IC) presents a significant leap forward in QC/QA of embankment, subgrade, sub-base and base course compaction for pavements, airfields, and transit [2]. CCC and IC move earthwork QC/QA from less than 1% coverage provided by spot test methods (e.g., nuclear moisture density gage) to 100% coverage. CCC also offers the potential to measure soil stiffness or modulus, i.e., mechanistic parameters that enable the implementation of performance based specifications.
While vibration-based measurement has shown much promise on smooth drum vibratory rollers, subgrade soils are often compacted more efficiently with pad foot rollers (FIG. 1) operated without vibration or ‘statically’. There is currently no CCC system for pad foot rollers that provides a measure of soil stiffness during static compaction. The only non-vibratory based measurement system is Caterpillar's machine drive power (MDP) approach that is based on propulsion power required to drive through soil during compaction. MDP has been empirically related to soil compaction [3, 4].
Current quality control/quality assurance practices often evaluate only 0.1% of the compaction area, which can be problematic for a heterogeneous material like soil. For example, in roadways, improper soil compaction can lead to potholes and cracking. The limitation in coverage is due to dependence on spot testing devices, such as the nuclear density gage or sand cone test. In addition to providing space coverage, these devices create a disparity between design and construction engineering by measuring density, whereas soil foundations are designed in terms of an elastic modulus and yield strength (i.e., stiffness and bearing capacity).
What is needed is a soil compaction device and methods for monitoring compaction with greatly increased coverage, using mechanistic measurements.